Regeneration of olefins from acid solutions



Allg 7, 1951 M. n. MANN, JR., ETAL REGENERATION OF OLEF'INS FROMHACID SOLUTIONS Patented Aug. 7, 1951 REGENERATION or charms Faoin` acm SOLUTIONS Matthew D. Mann, Jr.,

Mottern, Bloomfield, ard Oil Development of Delaware Roselle, and Henry 0.

N. J., aaslgnors to Stand- Complny, a corporation Application April 15, 1948, Serial No. 21,173 9 Claims. (Ci. 2641-677) This invention relates to a process for the recovery of olefin hydrocarbons from strong acid extracts of the corresponding alcohols or acid esters of the respective oleilns. More particularly, the invention deals with the recovery of the lower molecular weight olefin hydrocarbons, e. g. of the Cz to Cs range such as ethylene,

v propylene, isobutylene, n-butenes, and the lsomeric amylenes, etc., from acid extracts of their corresponding alcohols or acid esters. The desired olefinI ecovery is accomplished in this invention by passage of the acid extracts in long thin streams of definite length and cross-sectional area'under specific conditions of temperature, iiow rate, and acid strength to assure high yelds of the desired olefin in high purity.

The prior art discloses that oleilnic hydrocarbons can be prepared from the corresponding alcohols or acid esters by heating their acid solutions. The control over the reaction indicated by the prior art has been regulation of the temperature, acid strength and alcohol concentration. Some mention has been" made ofthe concentration of esteried oleiln present in the acid solutions. Disclosures of the prior art can be summarized by stating that the acid solutions are either (1) diluted, (2) maintained at a lower concentration by the presence of an excess of alcohol during distillation, (3) the distillation of the acid liquor is carried out in the presence of a salt, (4) acid liquor is heated to polymerize iso CF. The following patents are representative of the pror art: Engelhardt et al., 1,770,734; Deansley et al. 2,012,785; Snow 2,128,971; and Deansley 2,237,292.

The prior art does not disclose processes for recovery of oleilns. particularly isobutylene, in high yields from acid extracts containing acid at or closely approaching absorbing strength for the oleiln. Neither does it show a process for recovering olefin from an acid extract coincident with increasing the acid strength from somewhat below absorbing strength to absorbing strength. The teaching of the prior art that any suitable means of applying heat quickly to an acid extract will cause regeneration of oleiln is only correct when oleilns yields of less than are considered as proper demonstration of the art. It will be demonstrated in the examples that to maintain yields of oleiln above 5060% it is necessary to use the process described by this invention as contrasted to any process to be devised by implications from the prior art.

The olefin regeneration process as described in this invention differs from the processes of the prior art in that: (l) extremely large yields of oleiin, e. g. 80-90 weight percent and above. are obtained therefrom, (2) during the recovery process the acid strength is increased from somewhat below oleiin-absorbing strength up to olex tin-absorbing strength, thus requiring no restoration or reconcentration before being returned to the absorption system and (3) the purity of the regenerated olefin is extremelyhigh, e. g. llo-99% in the case of isobutylene.

It is an object, therefore, of this invention 'to provide an olefin recovery process in which high yields of recovered olen are obtained.

It is another object of this invention to prof vide a process for olefin recovery from their acid solutions in which the acid is recoveredfrom the regeneration in increased strength.

It is a further object of this invention to provide a process for olen recovery in which the purity of the recovered olen is extremely high.

'I'hese and other objects of the invention are accomplished by carrying out the regeneration according to the process which will now be set forth.

The practice of this invention will be described for illustrative purposes only using isobutylene and its sulfuric acid extracts as the reference materials. The acid extracts are prepared by the methods disclosed in the art. namely, acid treatment of a butane-butene fraction from petroleum or other sources under controlled conditions of temperature and pressure using -70% H2804. After the acid extract is settled free of the unabsorbed hydrocarbon, it is decanted and is ready for use in the isobutylene recovery process.

The isobutylene recovery is carried out as follows: Isobutylene acid extract is diluted with water from absorbing strengths of {iO-% to l5.5- 60% acid strength, calculated on a hydrocarbon free basis. 'I'he entrained and dissolved gases are allowed to disengage from the extract. The extract is then passed in long thin heated streams of restricted length and cross-sectional varea into uniform contact with a heat exchange surface,

preferably e. g. by passage through a tube-in shell heat exchanger under carefully controlled flash vaporization conditions, hereinafter described, which causes the isobutylene to regenerate from the acid extract. 'I'he isobutylene gas and acid effluent from the exchanger tubes are carried rapidly into a disengaging vessel Where the gas is taken overhead and the-acid ilows out the bottom through a cooler to a receiving vessel for recycling to the absorption unit. The lsobutylene passes from the disengaging vessel to conventional scrubbing, compression and fractionating equipment for purification. The process is thus adapted to continuous operation. The operation of the exchanger-generator is closely controlled as to acid extract flow rate, temperature, pressure, acid strength, extract saturation, etc., in order to minimize recovery of potential isobutylene as polymer or as alcohol.

Oraiulrmc CoNnxrIoNs v The acid extract is fed to the exchanger` tube' 3 at a rate which will maintain the entering liquid linear velocity at 0.4-2.0 ft./sec. for each stream entering the heat exchange surface. Velocities lower than 0.4 ft./sec. cause polymerization and velocities higher than 2.0 ft./sec. cause incomplete regeneration of the olein. 'I'he preferred range of velocity is inuenced partly by the saturation of the extract, viz. the mols olefin/mol acid. When the extract saturation is in the range of 0.2-.8 the preferred velocity is .4-.8 ft./sec. when the extract saturation is 0.8-1.0, the preferred velocity is .6-1.0 ft./sec. When the extract saturation is above 1.0 the preferred velocity is at 1.0-1.2 ft./sec.

The regeneration must be carried out at absolute pressures between 600-1000 mm. Hg. At pressures below 600 mm. too much of the olefin is recovered as the corresponding alcohol to give a. good yield per pass and can only be converted t olen by recycling to the process. At pressures over 850 mm. the yield of isobutylene is reduced through polymerization. Only at pressures close to atmospheric can the yield of olefin be held to a high figure, i. e., above 80 weight per cent.

The temperature of the reaction is measured at the outlet to the exchanger tubes. This tempera` ture is held at a point to indicate the boiling point of the acid at the desired strength. The temperature is'a function of the pressure, rate ot heat input and the partial pressure over the acid. The partial pressure is influenced by the quantity of olefin regenerated. For example, where temperatures of 150C. may be required to recover the acid at 65% from extracts of 0.5 saturation, extracts at 1.0 saturation give suiiicient gas to give 65% acid at 135 C. At the preferred rates of flow, the acid strength was held at 65%.

Although the regeneration to high yield is operable in the range of 60-70% eluent Aacid strength, the preferred range is ff-66%. The strength is suilicient for fast absorption rates and gives less polymerization in the exchanger generator. The dilution of the extract from the absorber is made to give 55-60% acid for regenerating isobutylene. The regeneration of ethylene, propylene or n-butylene is carried out at higher acid strengths and temperatures.

The length and diameter of the heated stream of extract must be limited to maintain a high yield of olen. When a tubular heat exchanger is employed in the process, these factors can be controlled, of course, by the length and diameter of the exchanger tubes themselves. 'Ihe length may preferably vary between 3 ft. and 10 ft. Tubes shorter than 3 ft. do not give enough surface and heat to insure complete regeneration or recovery of isobutylene. Tubes longer than ft. cause development of pressures above 5 lbs. inducing excessive polymerization. The diameter of the stream (or atleast one diameter in the case of non-circular streams) can vary between 1A" and 3A", assuring a ow velocity for a given extract in the proper velocity range as indicated above.

The following discussion illustrates the effect of operating variables on the overall process yields etc. as determined by actual plant runs on the regeneration of isobutylene from sulfuric acid extracts.

Errncr or LENGTH ANn DIAMETER or Ex'rmlcr STREAM One of the major variables affecting the yield of isobutylene by the flash exchanger-generator process is the diameter-length ratio of the extract stream, i. e. the diameter-length ratio of the exchanger tubes. A 1,42" diameter tube was chosen as the largest size 'in tantalum tubing which would not collapse under the external steam pressure. Copper was found to be equivaient in performance and was used in most of the experimental work. The tube length was varied at 3', 5' and 10' to explore the relationship between the volume of liquid feed and tube length. Lengthening the tube increased isobutylene yields at a given feed rate. Linear velocities below 0.3 ft./sec. show low yields of isobutylene for all tube lengths. At 0.4-0.8 ft./sec., regeneration yields approach a maximum for each tube length, This is shown in Table I following.

Table I Erreur or FEED Rare oN TUBE LENGTH p2" o. D.. m" I. D. copper mbe. Emmsamrauon-as. outlet temperature=l50 0.]

Tube Length Linear l Velocity, 3' 5 lo' ft./sec.

Weight Per Cent Iso C4(on Recovered Products) 0 l 60 5 75.0 0 2 56. 5 78. 0 8l. 5 0 3 63. 0 78 5 84. 0 0 4 63.5 80 0 8&0 0 s 64. o au o s4. 5

Maximum regeneration is approached for the 1/2" tube at a length 0f 10 fet. Data set out in Table II below on the yield at a given velocity show that an increase in tube length beyond 10 feet would have little or no further effect on yield.

Table II EFFECT OF TUBE LENGTH ON ISOBUTYLENE REGENERATION UQ" O. D., 7Ae I. D. copper tube. Feed rate=0.6 ft./sec. Extract saturation=0.5.]

Weight Per Cent Cr' Regenerated (on Recovered Products) Tube Length, Ft.

SUN

'see

OQQ

Polymer and alcohol formation are relatively constant over the range of practical feed rates- 13.5% polymer and 1.5% alcohol. This is illustrated in Table III:

Table III POLYMER AND ALCOHOL FORBATION I" O. D., Zie I. D.Xl0 it. Round Copper Tube. Extract satura- Weight Per Cent Isobutylene to Feed (on Reeove Rate, Products) lt./sec.

Polymer t-BuOH The small quantity of alcohol produced is contained in a. water layer from the condensed overhead stream. The entire water layer can be recycled to the initial dilution stage for reducing the effective acid strength of the extract to 60%. If a water balance is maintained only make-up water need be added to the dilution stage. Polymer composition is similar to that produced by current steam stripping regeneration technique. A typical analysis of the polymer produced from an extract containing 93 weight percent isobutylene and 7 weight percent normal butylene, 52.8% dimer, 22.7% trimer, and 24.5% codimer.

Tube diameters were varied between V1" and 11/2" for copper, Nichrome, and tantalum. The l/" O. D. (115" I. D.) tube was the largest diameter tubing used that gave no isobutylene in the spent acid. Too large a tube permits slugs of only partly heated extract to be blown through the tube before the olefin is adequately liberated. Since the V1' tubing seemed impractical for commercial use, the 1/2" was chosen for study. The data on the effect of tube diameter 0173 ft. lengths are summarized in Table IV, following.` It is apparent that the smaller the diameter, the greater is the regeneration of isobutylene.

Table IV EFFECT F TUBE DIAMETER ILength=3 ft. Feed rate=0.4-0.6 it./sec.]

Weight Per Cent Iso Cr to (on Recovered Products) Tube Inside Diameter Regen.

erared Isobutylene ISO CF il! t-BIOH spentAcid Polymer 905.3353 Ul Oooh* 0 0 0 32. (heated internally).. 33. 3

EFFECT 0F SHAPi: or Ex'rRAC'r STREAM DURING REGENERATION Flash regeneration of isobutylene requires a high rate of heat input combined with a short contact time. The shape of the surface over which regeneration takes place has been found to affect the rate of heating and the uniformity of flow over that surface with consequent effect on regeneration. 'I'his relationship was/,demonstrated by altering the shape of the extract stream, i. e. for example. the shape of the exchanger tubes.

A l/" tube, flattened to 1A" minimum diameter, showed higher yields than a round tube of similar length. A comparison of 3' and 5 tube lengths in both round and flat tubes is shown in Table V.

Table V EFFECT 0F TUBE SHAPE ON REGENERATION [Tubelength=3and .5'. Extractsaturation=0.5. Wrouud tube vs.

l tube flattened to l" minimum diameten] Weight Per Cent Iso C4 Reg. (on Linear Recovered Products) Velocity 3' Round 3 Flat 5 Round 5 Flat FL/sec Feed rate appears critical for the flattened tubes for a given length.

'I'he effect of flattening a 1,5" x 5 tube on regeneration was `equal to increasing the length of the cylindrical tube to l0 feet. Considerably higher yields were obtained for the :flattened tube in a feed rate range of 0.30.6.

Table VI EFFECT or TUBE SHAPE oN REGENERATION p5" o. D. cu Tube. Ruund vs. damned to u" minimum dismesse] Wlig'ht Per Ceti. (Iso i' regenen on Linear vered Products) Velocity 1o' Round s' Fm FL/lec.

y Table V11 EFFECT 0F FILLER BARS ON REGENERATION IM" I. D. tantalum round tube 3 long.]

Weight PerCent Iso C4- Re generated (on Recovered Flle:- Annular roducts) at Linear Vel. o. Space (ft/sec.) ol- Inches Inches 54 $6 65.0 62.5 He 60. 0 74.0 78. 5 "/e 56a 69. 5 80.0 88.5

Table VIII EFFECT 0F ANNULAR SPACE USING A TANTALUM THIMBLE lHeated internally] Weight Per Cent Iso C4- regenerated (on RecoveredProd- Linear ucts) Velocity W'Annular W'Annular Space Space Ft./sec.

summarizing the data on the effect of tube shape or surface phenomena on regeneration in heat exchange equipment, it is shown that a flattened tube gives the highestisobutylene yield for a given length. The limiting capacity for an exchanger of a given surface area appears about the same with round or flat tubes. Table IX summarizes data on the effect of tube shape on regeneration.

Table IX EFFECT OF TUBE SHAPE N REGENERATION The extract streams being subjected to heat exchange should preferably flow in a descending stream. For example. when exchanger tubes are employed they should be placed in a vertical position to insure even distribution of extract through each tube. A pool of extract above the tube bundles would provide uniform distribution through orifices into each tube. Carbate is recommended as a material for the distribution plate and should be thick enough to thermally insulate the extract above the orifices. When the extract streams were allowed to flow in a lateral direction poor yields of regenerated olen resulted. When the extract stream is subjected to heat exchange in an upfiow direction, extremely poor yields of regenerated olefin resulted. The poor yields in these instances are due, undoubtedly, to two factors, namely, the pressure required to promote proper flow of the extract stream, and secondly, the collection of acid which-occurs under conditions of lateral flow and up-ilow. The pressure employed is conducive to polymerization of the olefin, likewise, contact with acid at the temperature employed is conducive to polymerization which, of course, detracts from the yield of desired olefin.

EFFECT 0F EXTRACT SATURATION The saturation of the extracts employed in the olefin regeneration process is preferably between 0.5 and 1.5. Experiments were carried out employing saturations in the above regions. Extracts of 1.0 saturation were found to give on regeneration, yields of 83% at 0.6 ft./sec. feed rate. On increasing the extract saturation to 1.5, it was found necessary to increase the feed velocity to 1.1 ft./sec. to reach an 85% yield. The higher feed velocities were not necessary to secure good yields at the 0.5 saturation. At the higher extract saturation less steam pressure was necessary to maintain a spent acid strength of 65% H2504. indicating a greater steam emciency for regeneration. Table X summarizes data on the effect of extract saturation at various feed velocities on isobutylene regeneration.

8 Table x EFFECT EXTRACT SATURATION Ui" O. D., Mn" I. D. x 10 copper tube.]

Weight Per Cent Isobutylene (on Rec. Prod.) at Linear steam Per Cent sEtxtrzct Vel. of- Press H2804 in r a ura ion v s. i. s SApixt HsAr REQUIREMENTS Heat requirements for regeneration and acid concentration were determined by measuring the total condensed steam from the heat exchanger. A blank run was made for each experiment for equipment heat loss. The results showed that 3D0-375 B. t. u. per lb. 60% acid extract would be required over the range of 0.5-1.5 saturation. This includes heat required to raise the acid from 15-150" C., to regenerate the isobutylene and to increase the acid strength from 60% to 65%.

IsoBU'rYLnNn PUiurY Isobutylene purity is in a range of 96-99%. An extract feed containing 91.5% isobutylene and 8.5% n-butene yields isobutylene of 98.9% purity (by HC1 method) The normal olens are usually found as codimer in the polymer produced.

l Reactor pressure was maintained below 2.0 p. s. i. g. Previous laboratory work above this pressure showed that excessive polymerization occurred. Low pressure on the system was obtained by increasing the size of the outlet piping from the acid settler to reduce back-pressure.

Faim ExrxAcr Acrn STRENGTH Feed extract acid strength of close to 60 weight per cent H2804 (hydrocarbon free basis) was used in the regeneration of isobutylene. Previous laboratory studies indicated that 58-60 weight per cent feed acid (after dilution) gave higher yields and increased product purity.

SPnN'r ACID SrnnNcrn Spent acid strength was held at 65% by controlling outlet temperatures. No isobuytlene was present in the spent acid at optimum operating conditions. Nov further acid concentration of the spent acid is required for absorption. The spent acid is cooled and recycled directly. The strength of the spent acid was easily held during a wide range of operating conditions, i. e., feed rates 0.1-1.1 ft./sec., extract saturations of 0.5-1.5 and feed acid strength of 58-60%.

A very important part of the process for regenerating olens by the technique described is that the acid can be recovered in condition for recycling directly to the absorption step. 'The acid as recovered contains only traces of separable carbonaceous and polymeric hydrocarbon material and these traces are removed byA adequate settling facilities. Other processes requiring dilution and reconcentration steps often cause the inclusion of such materials in the acid of absorption strength and result in emulsion formation in the extraction step or foaming in the regeneration step. Acids recovered at recycling strength from the process described are clean enough to avoid such occurrences.

OUTLET Tnuelnsrunns Outlet temperatures were adjusted to maintain a spent acid strengthof 65% H2804. Extracts of 0.5 saturation were held at 150 C., 1.0 saturated at 145 C. and 1.5 extracts at 135 C. Temperatures were controlled -by varying steam pressure on the shell side of the exchanger. The temperature employed must be suchthat polymerization and other secondary reactions are avoided. The latter undesirable effects are presented by properly correlating the temperature with the contact time.

TUBE Maru.

Tantalum metal is recommended for the exlchanger tube construction. Tantalum was tested by lpassing 65% H2804 through a tube at a rate of ga11ons/hour-(0.ft./sec.) at 150 C. for 190 hours. No indication of corrosion or erosion was noted in this service. The experimental tube showed no signs of distortion under 125# external steam pressure.

or other sources under controlled conditions of z.'

temperature and pressure employing 60-70 weight per cent sulfuric acid.A This extract is diluted with water entering through line 3 until it reaches an acid strength of 55-60%. In the degassing drum entrained and less reactive. unabsorbed C4 hydrocarbons are removed via line 4. The temperature employed in the degassing drum is a temperature below that at which polymerization of the isobutylene or copolymerization of isobutylene-butene occurs. The extract is pumped from deg'assing drum via line 5 to regenerator 5. In the drawing the regeneration zone is illustrated as a vertical tube-in-shell heat exchanger of the conventional type. Numeral 1 represents the exchanger tubes which may vary in length, preferably between 3 and 1'0 feet as previously described and 1A to 3A" preferably 1/2" in diameter. The extract is rapidly heated by passage through the tubes at a pressure below 2.0 p. s. i. g. and linear velocity of 0.4to 1.2 ft./sec` The temperature during this passage is maintained at approximately the boiling point of the acid by circulation of steam or other fluid in indirect heat exchange with the extract by entrance through line 8 and exit through line9. For the regeneration of -isobutylene andV other tertiary olens such as tertiary amylene, a temperature in the range of 13G-160 C., preferably 140-155 C., is employed. Straight-chain oleiins of the C2 toCe range require higher acid strengths for absorption. Consequently, 'to maintain an acid of absorbing strength at the outlet of the heating zone higher temperatures are required, e. g. 165 C to 295 C., preferably 290 C. to 295 C. during ethylene regeneration, 165.C. to 278 C. during propylene regeneration, and 180 C. to 255 C. duringl n-Ci-Ce olen regeneration.

cohol and polymer vapor and liquid sulfuric'acid.

The gaseous mixture and acid emuent from the' 4 exchanger tubes are carried rapidly through line I0 into a disengaging drum II. It is essential that the evolved olefin be removed from the hot acid as quickly as possible to prevent excessive polymerization of the olefin. In this drum the gas is separated from the acid and removed from drum II via line I3. The acid settles and 1s removed via line I2. This acid becomes concentrated during passage through the regenerator and is restored to fio-70% concentration in which condition it is ready for re-use in the absorption of the (i4-hydrocarbon stream. The gas emerging from line I3 passes to a partial condenser I4 in which hydrocarbon polymers, alcohol and water are condensed and removed from the system via line I5. Isobutylene is withdrawn through line I 6 and countercurrently scrubbed in vessel I1 L-y dilute aqueous caustic for removal of traces of acid. The acid-free isobutylene is removed from vessel Il via line I8. It is then water-scrubbed, condensed and stored.

It will be apparent that a. system has: been described for the rapid uniform heating of the extract with low contact timeby passing it in fine streams at high velocity in contact with a heat exchange surface whereby the extract is decomposed and the isobutylene evolved therefrom. Although the flash evaporation process is preferably carried out employing the heat exchangergenerator described other means can be emplayed for providing a plurality of long unit paths of extract flow relatively thin in atleast one transverse dimension so that all the extract liquid is kept within a certain specified. distance at all times from the heat exchange surface.

'Another successful method employs a system whereby the extract is sprayed via a shower spray, or series of sprays, countercurrent to a uniform blanket of steam maintained at a temperature hotter than the boiling point of the extract, i. e. above C. for 65% H2SO4. Steam pressures of above about 54 pounds lgauge are required. In this operation the olen becomes disengaged from the decomposed extract and passes with the steam overhead from the settling acid. The gas is then separated, scrubbed and condensed as described above.

" In the regeneration zone conditions throughout are to be -closely controlled to attain best operation. Proper flow of the extract is necessary so that all parts of it receive substantially identical and immediate heat treatment. This is accomplished by proper association of the heating medium or heat transfer elements with the respective extract paths. Every part of the extract stream during its passage through the regeneration zone lies suilciently close to the heating medium or heat transfer element to insure uniformity of temperature throughout the extract during its brief passage through the regeneration zone. The tube-in-shell heat exchanger equipment is pref-erred for the process of this invention because the design and arrangement of the tubes within the shell is such Under these conditions the aqueous acid exthat the tubes seem to divide the body of extract entering the header thereof into a plurality of longitudinal streams .whose greatest length is parallel to the direction of extract flow, thus offering maximum resistance to lateral flow. The dimensions of the longitudinal streams should be 3 or more feet in length up to-l0 feet and between 1A" and 1% preferably t" in ditubes as indicated.

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As previouslysmted 51111110 exists t the nameter of the tube which is to be employed to pro-` duce the extract stream. It has been found that the diameter of the tube may be increased provided the tube is supplied with a filler bar. The data obtained from a series of runs indicate that 14 ticularly those of Cz to C9 molecular weight. It should be borne in mind that each olefin has its own optimum acid regeneration strength. For example, when regenerating ethylene from its sulfuric acid extract it is recommended that the extract be diluted no lower than about 85% acid high yields of regenerated oleiln may be obtained strength propylene not below about 65% acid by carrying out the regeneration in a tube supstrength; n-butenes not more than 60% acid plied with a illler bar. Data obtained are sumstrength; tertiary amylene and isobutylene not marized in the following runs: below about 55%. These dilutions are recom- Table XIII IsoBUTYLENE RE GENERATION FROM ACID Ex'rRAoT TUBULAR FLASH HEATER Wei ht Per Cent Conversions, Weight Per Cent Conversions, Total Material Balances, Weight Per Cent on otal 10004` Recovered 0 tin Recovered Charge mm No Total Sec IsoC" IsoCrto lsoCi-to Total t-BuOH Total auf Polymer Buon ggg? Polymer as olefin gaga 0101111 I SOC H150* H10 W I. D. Round Tantalum Tube-l-'l/a Brass Filler Bar x 3' Long 54 aan 10.8 2.3 00.0 15.0 2.1 1. 7 95.3 90.0 100. 2 104.0

M" I. D. Round Tantalum Tube+%" Brass Filler Bar x 3' Long 7&0 21.0 0.2 70.5 29.0 0.2 1.3 90. 7 95.5 101.0 105.5 7&5 19.0 1.0 71.9 23.9 1. 7 2.5 90.3 99.1 102.0 102.5 70.1 13.4 3.5 09.3 20.1 3.1 1.5 100.5 100.7 100.5 101.5

l" I. D. Round Tantalum Tube-H4 Brass Filler Bar x 3 Long 39 77.9 20.3 1.3 72.0 25.1 1.3 0.0 9z-7 90.1 107.3 150.0 as 77.3 19.3 2.4 75.2 22.4 2.1 0.3 99.5 93.3 100.0 102,3 93.0 5.0 1.9 89.0 8.5 1.7 0.3 99.5 98.1 95.5 119,0

y. I. D. Round Copper Tube x 3. Heated Surface=0.l53 sq. it.

TERrIAaY AMYLENE REGENERATION Two runs were carried out on the regeneration of tertiary amylene from acid extracts obtained b3 sulfuric acid absorption of a C5-refinery hydrocarbon stream. In the preparation of the C11-extract. sulfuric acid `of about 70% strength was employed in the absorption operation. This acid, is of course, a little higher than that used in the preparation of the C4-extract. The runs were carried out in the exchanger-generator apparatus as previously described employing a flattened tube of 1/2" minimum diameter copper tubes of 10 ft. length. Operating conditions and results obtained are summarized in the following table:

Table XIV.

Run No 1 2 Feed Extract Acid Strength (Diluted from 70% to 60%) 56. 7 57.0 Extract Feed Raie, liters/minute 0.932 0.62 Extract Saturator 0.370 0.278 Regenerator Outlet Temp., "C 159 162 S nt Acid Strength 69. 3 68. 4

ydrocarbon Content Spent Acid Product Analysis trace-tar trace-tar Weight Per Cent:

C1* 5.0 11.4 bCr-. 64. 2 58. 7 ll-Ct-- 12. 4 7. 9 5TH-1' i- 1 po yme 1 alcohol 5. 3 2. 5 Per Cent Regen. based on analysis of Product 91. 3 88.-()

Although the invention has been illustrated by the application oi.' the process to the regeneration of isobutylene and tertiary amylene the invention is equally applicable to other mono-olefins, parmended for practical yields of olefin, i. e., 70 weight per cent and above. When acid dilutions below these figures are employed oleiln yield is sacrificed to alcohol production which would. of course. be recycled to the regenerator feed. Sometimes under these conditions ethers form. particularly if pressure develops in the regenerator.' This, of course, promotes loss of oleiln yields.

Phosphoric acid, benzenesulfonic acid or salts yielding such acids may be employed in place of the sulfuric acid.

Mixtures of such acids may also be employed. In general polybasic mineral acids or polybasic mineral acid-acting substances may be employed for the Apreparation of the extract feed to the regenerator.

It will be apparent that the process of this invention is applicable to the evaporation of a vapor producing feed by submitting the feed in finely divided continuous streams of restricted length and cross-sectional area to constant and uniform heat exchange (direct or indirect) under controlled rates of flow, temperature etc.L

This is accomplished by providing preferably aample, the cross-sectional area may be circular, or non-circular. The non-circular area may be square, rectangular, elliptical, star-shaped etc., but preferably elliptical. However, according to the terms of the invention at least one diameter of the cross-sectional area must be within 1/4 to 3A for an unobstructed stream (i. e. as previously explained the diameterL may be increased if a filler bar is employed). Thus, the greatest distance of any particle from a heating surface or a heating medium will be 1/8" to In this manner the proper amount of heat is applied to the liquidrstream, uniformly, at the proper time and for the proper duration. This correlation oi conditions is conducive to the high yields of regenerated olefin.

The improved process covering the use of noncircular extract streams is not being claimed in this application but is the subject matter of another application namely, Serial No. 21,174 in the name of Francis M. Archibald and Vincent F.

, Mistretta filed of even date herewith.

Having described the invention in a manner so that it may be practiced by those skilled in the art, what is claimed is: y

1. A process for the regeneration of a monoolefin containing 2 to 6 carbon atoms per molecule from an acid extract thereof which comprises continuously passing the liquid extract downwardly at a linear velocity of 0.4 to 2.0 ft./sec. into one end of an externally heated cylindrical decomposition zone of 3 to 10 feet in length and 1/4 to 3A in inner diameter, maintaining the extract at a substantially uniform temperature between 130 C. and 295 C. during passage through the decomposition zone whereby the acid extract is decomposed to substantially a mixture comprising mono-olefin vapor, water vapor and liquid acid, continuously passing the total extract decomposition products from the other end of the decomposition zone into a disengaging zone and rapidly separating and removing said vapors from the liquid acid in the disengaging zone.

2. A process according to claim 1 in which the liquid acid extract is fed to the decomposition zone at a rate of 0.4 to 2.0 ft./sec.

3. A process according to claim l in which the extract is fed in a plurality of streams to a plurality of decomposition zones.

4. A process for the regeneration of a monoolefin containing 2 to 6 carbon atoms per molecule from an acid extract thereof which comprises continuously passing the liquid extract downwardly at a linear velocity of 0.4 to 2.0 ft./sec. into one end of an externally heated cylindrical decomposition zone of 3 to 10 feet in length and 1A to a/i in inner diameter, maintaining the extract at a substantially uniform temperature between 130 C. to 295 C. during passage through the decomposition zone whereby the extract is decomposed to substantially a mixture comprising mono-olefin vapor, water vapor and liquid acid, continuously passing the total extract decomposition products from the other end of 'the decomposit.on zone into a disengaging zone, rapidly separating and removing said vapors from the liquid acid in the disengaging zone, and recovering mono-olefin from said vapors.

5. A process for the regeneration of a tertiary mono-olefin containing 4 to 6 carbon atoms per molecule from a. sulfuric acid extract thereof which comprises continuously passing the liquid extract downwardly at a linear velocity of 0.4 to 2.0 ft./sec. into one end of an externally heated cylindrical decomposition zone of 3 to 10 feet in length and 1A" to 1% in inner diameter, maintaining the extract at a substantially uniform temperature between 130 C. and 160 C. during passage through the decomposition zone whereby the extract is decomposed to substantially a, mixture comprising tertiary mono-olefin vapor, water vapor and sulfuric acid, continuously passing the total extract decomposition products from the other end ofthe decomposition zone into a diseneasing zone, rapidly separating and removing said vapors from the sulfuric acid in the disengaging zone-, and recovering tertiary mono-olefin from said vapors.

6. A process for the regeneration of isobutylene from a sulfuric acid extract lthereof containing weight per cent sulfuric acid which comprises diluting the extract with water until it contains 55-60 weight per Icent acid, continuously passing' the diluted extract downwardly at a linear velocity of 0.4 to 1.2 ft./sec. into one end of an externally heated cylindrical decomposition zone of 3 to 10 ft. in length and 1A" to in inner diameter, maintaining the extract at a substantially uniform temperature between C. and C. during passage through the decomposition zone whereby the extract is decomposed to substantially a mixture comprising isobutylene vapor, water vapor and liquid sulfuric acid of 60-70 weight per cent strength, continuously passing the total extract decomposition products from the other end of the decomposition zone into a disengaging zone, rapidly separating and removing said vapors from the liquid acid in the disengaging zone, and recovering isobutylene from said vapors.

7. A process for the regeneration of propylene from a sulfuric acid extract thereof containing 'l0-92 weight per cen-t sulfuric acid which comprises diluting the extract with water until it contains 65-70 weight per cent acid, continuously passing the diluted extract downwardly at a linear velocity of 0.4 to 1.2 ft./sec. into one end of an externally heated cylindrical decomposition zone of 3 to l0 ft. in length and 1A" to in inner diameter, maintaining the extract at a substantiaily uniform temperature between C.- 278 C. during passage through the decomposition zone whereby the extract is decomposed to substantially a mixture comprising propylene vapor, water vapor and liquid sulfuric acid of 70-92 weight per cent strength, continuously passing the total extract decomposition products from the other end of the decomposition zone into a dislinear velocity of 0.4 to 1.2 ft./sec. into one end of an externally heated cylindrical decomposition zone of 3 to 10 feet in length and 1A," to 374, in inner diameter, maintaining the extract at a substantially uniform temperature lbetween 290 C. to 295 C. during passage through the decomposition zone whereby the extract is decomposed to substantially a mixture comprising ethylene vapor, water vapor and liquid sulfuric acid of 93-98 weight per cent strength, continuously passing the total extract decomposition products from the other end ol' the decomposition zone into a dsengaging zone, rapidly separating and removing said vapors from the liquid acid in the disengaging zone, and recovering ethylene from said vapors.

9. A process according to claim 4 in which the extract is fed in a plurality of streams to a plurality of decomposition zones.

MATTHEW D. MANN, Jl. HENRY O. MO'I'I'ERN.

I8 REFERENCES CITED The following references are of record in the file of this patent:

Number l o Number UNITED STATES PATENTS Name Date Deane/sly et al. Jan. 3, 1939 FOREIGN PATENTS Country Date Great Britain Feb. 26, 1931 Great Britain July 25. 1940 

1. A PROCESS FOR THE REGENERATION OF A MONOOLEFIN CONTAINING 2 TO 6 CARBON ATOMS PER MOLECULE FROM AN ACID EXTRACT THEREOF WHICH COMPRISES CONTINUOUSLY PASSING THE LIQUID EXTRACT DOWNWARDLY AT A LINEAR VELOCITY OF 0.4 TO 2.0 FT./SEC. INTO ONE END OF AN EXTERNALLY HEATED CYLINDRICAL DECOMPOSITION ZONE OF 3 TO 10 FEET IN LENGTH AND 1/4'''' TO 3/4'''' IN INNER DIAMETER, MAINTAINING THE EXTRACT AT A SUBSTANTIALLY UNIFORM TEMPERATURE BETWEEN 130* C. AND 295* C. DURING PASSAGE THROUGH THE DECOMPOSITION ZONE WHEREBY THE ACID EXTRACT IS DECOMPOSITION ZONE WHEREBY THE MIXTURE COMPRISING MONO-OLEFIN VAPOR, WATER VAPOR AND LIQUID ACID, CONTINUOUSLY PASSING THE TOTAL EXTRACT DECOMPOSITION PRODUCTS FROM THE OTHER END OF THE DECOMPOSITION ZONE INTO A DISENGAGING ZONE AND RAPIDLY SEPARATING AND REMOV- 